There is a demand for detectors and microphones which translate any kind of acoustic signal, e.g. sound, noise, vowels, speech, voices, into electrical signals.
Examples for acoustic detector systems are hearing aids which receive and amplify acoustic signals and generate an amplified acoustic signal which can be fed into the outer ear, or special hearing aids which apply electric signals to the inner part of the ear by means of electrodes such that certain segments of the ear are stimulated. The stimulation of the ear by means of electrodes, implanted into the ear, is often used if a person is deaf or partially deaf. Nowadays, in certain cases electrodes are even implanted into the inner ear directly contacting the nerves of the ear. Current hearing aids rely on a conventional microphone the output signal of which is amplified and fed via a speaker into the outer ear. In case of electrodes being implanted into the ear or even in proximity of the hearing nerves a processor is employed to process the electrical signal output by a microphone in order to generate electrical pulses which can be fed to the electrodes. The processing is very complex and such hearing aids which are designed for implantation into the human ear are currently expensive and not very powerful. Usually, only twelve electrodes are employed to stimulate the nerves in the inner ear. It is obvious that such a system stimulating the ear only with a small number of electrodes never will reach the capabilities of a healthy, fully functional human ear. Accordingly, there is a demand for a detector or microphone that really simulates the function of the human basilar membrane and inner ear and thus may serve as a replacement for a destroyed or defective organ of hearing.
Speech detection and recognition systems are another field where acoustic detectors (microphones) can be used. Speech recognition system are currently used to simplify input of commands or text into a computer, for example. Also handicapped persons rely more and more on technical and electrical apparatus which can be operated by giving acoustic commands. Furthermore, pilots, car-drivers, technicians, and surgeons will use such speech recognition systems as they become more powerful and reliable.
Todays speech recognition systems rely on conventional microphones which are used for transformation of acoustic signals into electric signals which are then processed and analyzed in the frequency domain. These electric signals are then fed to a processor which tries to recognize letters, syllables, words and whole sentences. These systems require lots of computing power because complex analysis are carried out and a comparison with a speech data base (knowledge base) is required. An enormous amount of incoming data is to be processed within a short period of time to ensure an acceptable response time and reliable recognition.
There is also a great demand for acoustic detectors which are designed to detect a particular noise or sound. Such a detector could for example be used to indicate whether an engine is about to get destroyed, or to detect acoustic signals which can otherwise not be detected by the human ear. In noisy environment, e.g. in a cockpit, it would be useful to reduce or eliminate the noise so as to ensure that voice and other signals can be better understood. Such detectors which are sensitive to a particular noise are usually realized by means of a conventional microphone, or a microphone which is sensitive in the particular range of frequencies, followed by an electronic circuitry or computer for analysis of the electric signals output by the microphone. Currently, there is a trend towards cars having an active microphone/loudspeaker system for the suppression of noise entering the passenger compartment. By means of a microphone the noise of the tires, for example, is collected and transformed into electrical signals. These signals are then amplified and phase-shifted before they are converted back into acoustic signals by means of a set of loudspeakers. The superposition of the original noise and the phase-shifted noise leads to a reduction in the overall noise level.
As can be seen from the above examples, most of the known systems for the detection of sound, noise, vowels, speech, voices, etc., employ an electronic circuitry or computer for processing and analysis of the electrical signals provided by a conventional microphone.
In order to further improve such systems and to make them cheaper, one needs smaller microphones and detectors. In addition, such microphones and detectors should be cheap, reliable and lightweight. In particular those systems which require analysis of acoustic information, e.g. speech recognition systems, call for time-consuming processing by a computer or the like. The success and price of such systems strongly depends on a simplification and improvement of known approaches.
As reported in the art, micromechanical elements are suited to replace conventional microphones and sensors. A micromechanical microphone, for example, is described in "A New Condensor Microphone in Silicon", J. Bergqvist et al., Sensors and Actuators. A21-A23, 1990, pp. 123-125. This microphone functions almost like a conventional microphone, with the difference that it is much smaller. In another article with title "Silicon Micromechanics: Sensors and Actuators on a Chip", R. T. Howe et al., IEEE Spectrum, July 1990, pp. 29-35, and in particular on page 31, it is mentioned that microvibrating beams, like a guitar string, react to a change of tension by a shift in its resonant frequency. This is an effect which probably allows to realize a microphone using such a vibrating beam being sensitive to noise. The shift in resonant frequency could be detected and transformed in an appropriate electrical signal for further processing. In the German article "Mikromechanik--Der Chip lernt fuhlen", A. Heuberger, VDI nachrichten magazin, 4/85, pp. 34-35, it is mentioned that an integrated sensor with a number of silicon beams, matching certain resonant frequencies, could be realized. However, it is mentioned at the same time, that such an integrated sensor will require a computer based analysis of the signals generated by the silicon beams.
The above three examples show that conventional microphones will be replaced by micromechanical structures in the near future. Such a miniaturization is welcome and leads to improvements of conventional systems and might even open up certain new opportunities because of its reduced size and price. However, there is still an immense amount of processing required for most of the above applications
There is also a demand for systems performing pattern recognition of electrical signals, in the range of 1 Hz to 1 MHz, as well as for systems processing and analysing mechanical forces in a reliable and fast manner.
It is an object of the present invention to provide a method and apparatus for reliable processing of acoustic, mechanical, and electrical signals.
It is an object of the present invention to provide a method and apparatus which improves known acoustic detectors and microphones.
It is an object of the present invention to provide a new approach for the detection, transformation and processing of acoustic signals and to provide systems based on this new approach.
It is another object of the present invention to provide a new approach for the analysis of acoustic signals and to provide systems based on this new approach.
It is a further object of the present invention to provide improved hearing aids, speech recognition systems, and sound, noise, vowels, speech, and voices detectors and noise eliminators.